The automotive industry has turned to the use of interior trim components such as door panels and comprising a polyvinylchloride shell. These components are utilized because they permit a wide latitude in styling and color, and grain effects which are most desirable in the interior design of automobiles. The current state of the art includes pre-formed grained vinyl shell made from dried thermoplastic powdered particles which are applied to a heated shell mold from a powder box to form a continuous one-piece shell. Such is illustrated in U.S. Pat. No. 4,562,025, issued Dec. 31, 1985 in the name of Gray.
These types of shells have also been used for instrument panels having an air bag deployment system therein, such as illustrated in U.S. Pat. No. 5,161,819, issued Nov. 10, 1992, assigned to the assignee of the subject invention. Typical air bag doors having a vinyl layer matching the outer vinyl layer of the instrument panel. Such vinyl layers are bonded to a layer of urethane foam at an interface. The vinyl and foam define a cover for an insert that includes either a single hinged door or a pair of doors that remain closed until an air bag is deployed. One problem with such constructions is that the vinyl material is thermoplastic. At elevated temperatures, such as occur on sunny days, the vinyl layer will have increased elongation properties. Thus, when the door or doors are swung open, upon inflation of an air bag, they will direct a separation force on the vinyl layer causing it to elongate. Such elongation will cause the vinyl layer to separate from the foam and from a bubble that balloons outwardly from the foam such "ballooning" at high temperatures, as the door is opened, can cause foam particles to separate from the foam layer as the foam and vinyl layers are separated at tear lines defined by the edges of the door or doors.
It is also known to add materials to or provide additional layers to vinyl materials to change the properties thereof, such as for strengthening. U.S. Pat. No. 4,900,489, issued Feb. 13, 1990 in the name of Nagase et al discloses a method for forming a skin foam article wherein the mold is filled with powdered polyvinyl chloride and fused together within the mold, and a second layer of expandable powder is dumped thereon. The mold is heated to expand the expandable powder, cooled, and the article demolded.
U.S. Pat. No. 4,610,835, issued Sep. 9, 1986 in the name of Ghavamikia, and U.S. Pat. No. 4,957,684, issued Sep. 18, 1990 in the name of Kia, both disclose fiber reinforced panels.
The '835 patent discloses a method of making a smooth surface with glass fibers therein. The method is practiced by coating the surface of a premolded glass fiber mat reinforced plastic panel maintained at room temperature with a room temperature curable polyurethane composition, and applying molding pressure on the coated surface to cause the coating resin to flow and fill the valleys between the glass fibers.
The '684 patent discloses the use of a fiber reinforced mat in a mold cavity. The disclosed method includes pouring a polymeric material into the cavity, saturating the glass fiber mat, closing the two mold members together with at least one layer of the flexible sheeting material disposed over and adjacent the interior mold surface, clamping the molds together, and curing the polymeric material for a time to harden the plastic panel.
The use of reinforced glass fibers in vinyl shells for instrument panels and other covers for air bag assemblies has been found unsuitable since glass fibers read through the outer (visually observed) surface of the air bag cover and cause a shimmery appearance.